Fire, historically more frequent and widespread, has been a key factor in shaping the ecology of the American Southwest. Native plant species evolved in tune with periodic fires and evolved adaptations to fires that occur at a particular frequency, season, and extent. Fire influences ecosystem processes and patterns, such as nutrient cycling and plant community composition and structure. Fire regimes in the American Southwest changed dramatically with the arrival of European and American settlers, whose livestock removed grassy fuels that carried fires and whose roads fragmented the continuity of fire-carrying fuels. Fires that did break out were suppressed. Systematic fire suppression continued in more recent years and further curtailed natural fire regimes. As a result, single, large-scale catastrophic fires now play a larger role in ecosystem functioning and can result in adverse effects such as erosion, loss of seed sources for natural regeneration of tree species, wildlife habitat loss, and increased insect and disease epidemics. A goal of the NPS is to restore fire’s role as a dynamic and necessary natural process.